38 Scientific Proceedings, Royal t)iihliii Society. 



diagnostic chai-acter; but it was clear that, on the average, the si)orangia of the 

 Enghsh, American, and Swiss fungi and of /'. C'adorum were considerably smaller 

 than those of P. Fagi, whilst those of the Irish fungus and P. Syringae were 

 intermediate in size. 



There was also considerable variation in the abundance of sporangium forma- 

 tion ; but it was clear throughout the work that the Irish fungus and P. Syringae 

 formed sporangia on the various media tried with considerably more reluctance 

 than the five others did. 



Having regard to all the characters shown in cultural and inoculation trials, 

 it was found impossible to distinguish between the English, American, and Swiss 

 Phytophthoras and the P. Cadoruvi stated to have been isolated by Peters from 

 Cactus seedlings ; and it is believed that the authors mentioned, who described 

 the rotting of apples and pears in the instances coming under their notice as being 

 due to P. Cadorum, were perfectly correct in so doing. 



That P. Fcuji and P. Cadorum should not be grouped together under the 

 name P. omnivora has already been pointed out by Himmelbaur.^ The present 

 investigations confirm this view. The sporangia of P. Vagi were found on the 

 average to be distinctly longer than those of P. Cadorum. Moreover, P. Fagi was 

 found incapable of infecting living specimens of Sempervivuvi arhoreurii-ridrum, 

 S. Bertlulotianum. and a species of Mammilaria, whilst P. Cadoriim was patho- 

 genetic to, and caused a rot in these plants. 



As the cultural work progressed it became clear that the Irish fungus was 

 neither P. Cadonun nor P. Fagi. On the other hand, it seemed to be closely 

 allied to, if not identical with, P. Syringae. Hence, careful parallel cultures and 

 inoculation experiments with the latter species and the Irish fungus were made, 

 with the result that no essential ditfereirces could be found between them. 



The rot produced by inoculating P. Syringae. into healthy apples was similar 

 to that originally found in the Irish apples. Further, the Irish fungus and 

 /'. Syringae when inoculated into buds of Syringa vulgaris caused identical forms 

 of rot; and oospores of identical character were developed in the dead tissues in 

 both cases. Hence it is concluded that the Phytophthora which caused the rot 

 in the Irish apples- is P. Syringae ; and it is believed that this is the first record 

 of attack by this species on apples, at any rate in Ireland. '- 



V. — Classification of Phytoplitlioras. 



The penetration of the antheridium by the oogonial incept and the develop- 

 ment of the oogonium proper on the summit of the antheridium in Phytophthoras 

 were first established with certainty in the case of P. erythrosejjtica.'^ At the same 

 time, this method of development of the sexual organs was found to occur in 

 P. infestans and P. Phaseoli, while it was surmised (correctly, as has since been 

 shown by Eosenbaum) to occur also in P. Arccae. In the paper referred to, and in 



■ See foot-note, p. 35. 



- There is some reason to believe that F. Syringae occurs in Ireland on Syringa vulgaris. 

 On two occasions within the past two years diseased Lilac leaves have been forwarded for 

 examination on "which a Phytophthora was present which, there was every reason to suspect, 

 was P. Syringae ; but the material submitted was not sufficient or suitable for raising cultures 

 and thus determining the species with certainty. Rosenbaum's statement (Journ. Agric. 

 Research, viii, 1917, p- 235), that he worked with P. Syriwiae isolated from Lilac in Ireland, is 

 an error. Nor was his culture of P. Fagi derived from Fagus seedlings in Ireland. 



2 Sci. Proc. Roy. Dublin Soc, xiii (N. S.), No. 35, 1913, p. 529. 



